The present invention relates to an apparatus and a method for fabricating a semiconductor device; and more particularly, to a thermal treatment apparatus capable of preventing a wafer from warping and a thermal treatment method using the apparatus.
In the process of fabricating a semiconductor device, thermal treatment is essential. Thermal treatment is used in the process of fabricating a semiconductor device for various reasons. For example, in case of oxidizing a silicon wafer, making it into a silicon oxide film (SiO2) and using it as an insulation layer, an etching mask or a gate oxide film of a transistor, thermal treatment is used for an annealing process of thin films and a reflow process for planarizing flowable films like a Boro-Phospho Silicate Glass (BPSG) film. Also, thermal treatment is used for an alloy process of an ohmic contact, an annealing process for curing ion implantation damage and activation of ion-implanted impurities.
The apparatus for performing such a thermal treatment is a horizontal or vertical furnace. Recently, a rapid thermal treatment approach is now being used to reduce the entire thermal budget of the fabricating process as the semiconductor devices become highly integrated. The rapid thermal treatment approach, which achieves the desirable effect by using a high temperature for a short time, is much used in semiconductor fabricating process since it can perform most of the various processes which are performed in the furnace and have the merit of minimizing the side effect of impurities being spread on a wafer.
Several methods for further increasing the operating speed of a semiconductor device along with making the device small are suggested and practiced. Among them, a method of forming a metal wiring layer into multi-layers is suggested, and a triple-metal stack structure is much used recently. As the height of a metal wiring layer increases as such, the stress inflicted on a thin film stacked at the lower side increases. Due to the accumulated stress, a wafer warps. This phenomenon has been raised as a serious problem.
The warpage of the wafer frequently occurs during a series of processes of forming a pattern on a bare wafer in an early state and depositing a thin film thereon. That is, the warpage of a wafer occurs due to the partial difference in pattern density in the process of fabricating a device or the difference in deposited film thickness and the accumulation of stress between the deposited films. Also, as the metal wiring structure has been changed to the triple-metal stack structure for the improvement of scaling down and operating speed of a semiconductor device, this phenomenon has become severe.
If the warpage of the wafer occurs, defocus is induced in the photolithography process for forming patterns on the wafer. If this becomes severe, a chuck which fixes a wafer cannot fix a wafer any more so that the process can't further proceed. It is especially true when highly integrated semiconductor devices have line width of less than 80 nm. Although experiments including changes of the film stress are being made to improve this matter, none of them has reached a satisfactory level.